Jared Fogle's Back in the Food Biz

Jared Fogle -- who was beaten by a prison inmate -- has learned revenge is best served cold ... and is doing just that at the prison cafeteria.

We've learned the former Subway pitchman was assigned cafeteria duties at Federal Correctional Institution Englewood. His principal duty was serving sandwiches at the end of the line. Our sources say prison officials were privately giggling over the irony.

The problem ... inmates felt Fogle was getting celebrity treatment with a cushy job, and especially after he was beaten up in January, so officials decided to move him from the inmate cafeteria.

Fogle's fellow inmates can't be happy about this ... he got what you might call a promotion. Now he's serving food at the correctional officers' cafeteria, which has higher-end food, including steaks.